Oracle has evolved over time to much more than just a plain relational database. One option is to use Oracle as an expensive calculator.
When researching or demoing Oracle, it’s quite convenient to do number calculations directly on sqlplus prompt, especially if dealing with internals where lots of stuff is about addresses and offsets shown in hex.
Here’s the script what I use for such purposes: https://github.com/tanelpoder/tpt-oracle/blob/master/calc.sql.
It usually saves me couple of seconds every calculation as I don’t have to reopen the calc.

How many times have you seen a following case, where a user or developer complains that their Oracle session is stuck or running very slowly and the person who starts investigating the issue does following:

Checks the database for locks

Checks free disk space

Checks alert log

Goes back to the client saying “we did a healthcheck and everything looks ok” and closes the case or asks the user/developer to contact application support team or tune their SQL

The point here is that what the heck do the database locks, alert log or disk space have to do with first round session troubleshooting, when Oracle provides just about everything you need in one simple view?

While reading the book 'Deep Survival' (most kindly given to me at the UKOUG conference in Birmingham by Sir Graham Wood of Oracle after the fire in my house) I happened on a description on page 107 of a book called 'Normal Accidents' by a fellow named Perrow (get it? per row - a perfect name for database nerds).

Perrow's theses is that in any tightly coupled system - in which unexpected interactions can happen - accidents WILL happen, and they're NORMAL.

Also, he states that technological steps taken to remedy this will just make matters worse.

Perrow and IT systems=====================I have freely translated Perrow's thoughts into the following:

IT systems are tightly coupled. A change - a patch, a new application, or an upgrade - to a layer in the stack can cause accidents to happen, because they generate unexpected interactions between the components of the system.